Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
CH Temperature Control set to approx. 12 o'clock position
Attach pressure gauge to gas valve pressure outlet test point
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow burner to ignite and establish.
Burner pressure will slowly ramp up to maximum after approx. 1 minute.
Once the CH flow temperature reaches approx. 60°C
does the burner pressure start to modulate down?
Note:
When pressure gauge is removed the pressure test point
should be tightened and checked for gas tightness.